1. Field
The present invention relates to a lithographic apparatus, a method for manufacturing a device and an apparatus manufacturing method.
2. Background
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
Electrostatic clamps may be used in lithographic apparatuses operating at certain wavelengths, e.g. EUV, since at these wavelengths, certain regions of the lithographic apparatus operates under vacuum conditions. An electrostatic clamp may be provided to electrostatically clamp an article, such as a mask or a substrate to an article support, such as a mask table or a wafer table, respectively. Conventional electrostatic clamps comprise a stack in which an electrode is disposed between an upper (first) and a lower (second) dielectric or isolating layer. For example, the lower layer is polished, then the electrode is deposited on the upper polished surface. Then the upper layer is placed on top of the electrode. The upper and lower layers are bonded together with, for example, anodic bonding. The electrode may comprise a plurality of portions. Particles on an upper surface of the electrode lead to unacceptable stresses in the upper layer after the bonding step. Further, the electrodes do not necessarily cover the entire surface of the lower layer. At some places no electrode may be present. This may result in small, but relatively long, gaps that can fill with one or more contaminants, such as air, dirt, a fluid or a combination thereof. In any of these cases, this may lead to unacceptable stresses in the upper layer, which may result in damage to the article or breakthrough between the different electrode portions, eg. a short circuiting of the electrode. Further, a contaminant may becomes trapped in the stack between the layers. When the clamp is subject to differing pressure environments, in particular, the upper layer may suffer from alternating forces which may lead to damaging of a layer.